Directions
Prepare a medium-hot fire in a charcoal grill with a cover, or preheat a gas grill to medium-high.

To make the patties, combine the chuck, ground sirloin, onion, garlic, and seasoned salt in a large bowl, handling as little as possible. Shape into 6 patties to fit the bun size. When the grill is ready, brush the grill rack with vegetable oil. Place the patties on the rack; cover, and cook, turning once, until done to preference, 5 to 7 minutes on each side for medium. Place the cheese slices on the patties during the last 3 minutes of grilling. Place the buns, cut side down, on the outer edges of the rack to toast lightly during the last 2 minutes of grilling.
Meanwhile, in a small bowl, combine mayonnaise, orange juice concentrate, celery and walnuts; set aside.

To assemble the burgers, place a cheese-topped patty on bottoms of rolls. Top with an apple slice and arugula. Spread chunky mayonnaise generously on roll tops. Add the tops to burgers and serve immediately.